1. Field of the Invention
The present invention relates to a liquid crystal display device and more particularly relates to a liquid crystal display device suitably used for portable information terminals (for example, PDAs), mobile phones, car-mounted liquid crystal displays, digital cameras, PCs, amusement equipment, TVs and the like.
2. Description of the Related Art
The information infrastructure is advancing day to day, and equipment such as mobile phones, PDAs, digital cameras, video cameras and car navigators has penetrated deeply into people's lives. Liquid crystal display (LCD) devices have been adopted in most of such equipment. With increase of the information amount handled with the main bodies of the equipment, LCD devices are requested to display a larger amount of information, and are demanded by the market for higher contrast, a wider viewing angle, higher brightness, multiple colors and higher definition.
A vertical alignment mode using a vertically aligned liquid crystal layer has increasingly received attention as a display mode enabling high contrast and a wide viewing angle. The vertically aligned liquid crystal layer is generally obtained using a vertical alignment film and a liquid crystal material having negative dielectric anisotropy.
For example, Japanese Laid-Open Patent Publication No. 6-301036 (Literature 1) discloses an LCD device in which an inclined electric field is generated around an opening formed in a counter electrode that faces a pixel electrode via a liquid crystal layer, so that liquid crystal molecules surrounding liquid crystal molecules existing in the opening, which are in the vertically aligned state, are aligned in inclined directions around the opening as the center, to thereby improve the visual angle characteristics.
However, in the device described in Literature 1, it is difficult to generate an inclined electric field over the entire region of each pixel. Therefore, each pixel has a region in which liquid crystal molecules delay in response to a voltage, and this causes a problem of occurrence of an afterimage phenomenon.
To solve the above problem, Japanese Laid-Open Patent Publication No. 2000-47217 (Literature 2) discloses an LCD device in which a plurality of openings regularly arranged are provided in a pixel electrode or a counter electrode, to form a plurality of liquid crystal domains each having axisymmetric alignment in each pixel.
Japanese Laid-Open Patent Publication No. 2003-167253 (Literature 3) discloses a technology in which a plurality of projections are provided regularly in each pixel to stabilize the aligned state of liquid crystal domains having radially inclined alignment formed around the projections. This literature also discloses using an inclined electric field generated at openings formed in an electrode, together with the alignment regulating force of the projections, to regulate the alignment of liquid crystal molecules, and thus improve the display characteristics.
Japanese Laid-Open Patent Publication No. 11-242225 (Literature 4) discloses a vertically aligned LCD device (MVA LCD device) having a plurality of slits (openings or cuts) extending in parallel with one another and projections or depressions formed in an electrode in each pixel.
In recent years, a type of LCD device providing high-quality display both outdoors and indoors has been proposed (see Japanese Patent Gazette No. 2955277 (Literature 5) and U.S. Pat. No. 6,195,140 (Literature 6), for example). In this type of LCD device, called a transflective LCD device, each pixel has a reflection region in which display is done in the reflection mode and a transmission region in which display is done in the transmission mode.
The currently available transflective LCD devices adopt an ECB mode, a TN mode and the like. Literature 3 described above also discloses adoption of the vertical alignment mode for, not only a transmissive LCD device, but also a transflective LCD device. Japanese Laid-Open Patent Publication No. 2002-350853 (Literature 7) discloses a technology in which in a transflective LCD device having a vertically aligned liquid crystal layer, the alignment (multi-axis alignment) of liquid crystal molecules is controlled with depressions formed on an insulating layer. The insulating layer is provided to make the thickness of the liquid crystal layer in a transmission region twice as large as that in a reflection region. According to this literature, the depressions are in the shape of a regular octagon, for example, and projections or slits (electrode openings) are formed at positions opposed to the depressions via the liquid crystal layer (see FIGS. 4 and 16 of Literature 7, for example).
In the devices having openings and/or cuts in electrodes in pixels as described in Literature 1 to 4, problems such as overetching and peeling off of a conductive film constituting the electrodes may occur in formation of the openings and cuts by etching, and as a result, the electrodes may be cut off and regions having no voltage supply may be formed. Formation of regions shut off from supply of a predetermined voltage in pixels will be recognized as display defects (black points in normally black mode display).
Also, when openings or cuts (electrical alignment regulating structure) and projections and depressions (physical alignment regulating structure) are provided as alignment regulating structures as described in Literature 1 to 7, liquid crystal molecules near such alignment regulating structures are inclined more greatly (closer to the horizon) than liquid crystal molecules in the other regions. Regions having such alignment regulating structures are therefore observed as brighter than the other regions in normally black display. In particular, the physical alignment regulating structures, which use the effect of the shapes of the projections and depressions and the like, exert their alignment regulating forces even during non-voltage application. Light leakage therefore occurs even in the black display state and this causes decrease in contrast ratio.
In view of the above, a major object of the present invention is providing a liquid crystal display device in which occurrence of display defects caused by cutting off of electrodes in pixels, which may otherwise occur when openings or cuts are formed in the electrodes, is prevented. Another object of the present invention is providing a liquid crystal display device in which reduction in contrast ratio due to light leakage, which may otherwise occur with alignment regulating structures formed in pixels, is suppressed.
Yet another object of the present invention is providing a transflective liquid crystal display device having a transparent dielectric layer in each reflection region, which has improved display quality.